1. Field of the Invention
The present invention is directed to a multiple electrode unitary intravascular catheter designed for use in a system which continually monitors heart function and, upon detection of abnormal function, provides either pacing energy or cardioverting energy as required. The unitary intravascular catheter is in one or more ways more versatile, more compact or more easily implanted than previous multiple electrode systems capable of functioning in the same modes. Additionally, the unitary catheter, which comprises a distal electrode, an intermediate electrode, and a proximal electrode, provides superior sensing capability immediately following cardioversion as compared to the prior art two-electrode catheters. Where a modified cardioverting energy distribution is required, the single intravascular catheter may be used in conjunction with other electrodes, such as a patch electrode applied to the external surface of the heart.
2. Description of the Prior Art
During the past several decades, coronary heart disease has become the primary cause of death in the developed areas of the world. Close to 1.5 million Americans will suffer a heart attack this year, with nearly 350,000 of them dying suddenly following the myocardial infarction. Although the precise cause of sudden death in coronary heart disease has not yet been entirely clarified, the available evidence permits the medical field to ascribe death in the majority of sudden death cases to rapid disturbances in cardiac electrical activity known as tachyarrhythmia. Tachyarrhythmic heart conditions which may be lethal, are ventricular tachycardia, ventricular flutter, and ventricular fibrillation. Atrial tachyarrhythmic conditions such as atrial tachycardia and fibrillation only become life threatening when they lead to rapid ventricular disturbance.
Excessively slow rhythm disturbances, known as bradyarrhythmias, are involved in a minority of cases. Bradyarrhythmic conditions become serious when there is a defect in impulse formation or in the normal cardiac conduction system without adequate "escape" rhythm.
Within the hospital environment, recent experience has demonstrated that tachyarrhythmic conditions are often reversible phenomena and may be corrected by applying relatively high energy electrical shocks to the heart. Bradyarrhythmic conditions, although not as often fatal, are often correctable by pacemaking pulses of very low energy. The correction of arrhythmic heart conditions by application of relatively high energy electrical shock to the heart will, for the purposes of this invention, be referred to as "cardioversion".
In recent years, substantial progress has been made in the development of techniques for effectively terminating various tachyarrhythmias. Recent developments include implantable electronic standby defibrillators which, in response to the detection of an abnormally rapid cardiac rhythm, discharge sufficient energy via electrodes connected to the heart to depolarize and restore the heart to normal cardiac rhythm.
Considerable sophistication now exists with regard to techniques for reliably monitoring heart activity in order to determine whether cardioversion is necessary. Included among such techniques are those which monitor ventricular rate to determine the presence of fibrillation on the basis of a probability density function (PDF), a technique described in commonly owned U.S. Pat. Nos. 4,184,493 and 4,202,340, both of Langer et al, and a more recent system which is disclosed in commonly owned co-pending application Ser. No. 175,670 of Langer et al, filed Aug. 5, 1980, now abandoned, utilizing both the PDF technique to determine the presence of an abnormal cardiac rhythm and a heart rate sensing circuit for distinguishing between ventricular fibrillation and high-rate tachycardia, on the one hand, and a normal sinus rhythm or low-rate tachycardia, on the other hand.
Commonly owned, co-pending application Ser. No. 478,038 of Imran et al, filed Mar. 23, 1983, discloses a cardioversion system including an implantable defibrillator and an external non-invasive controller/monitor for altering the state and/or retrieving status information from the implanted defibrillator. The implantable defibrillator comprises a high-voltage inverter circuit with shunt-prevention means; a combination of a PDF circuit and a heart-rate analysis circuit, each circuit detecting abnormal cardiac rhythms and both circuits jointly activating the high-voltage inverter circuit; a plurality of electrodes connected to the heart, including bipolar sensing electrodes, coupled with the heart-rate analysis circuit, for sensing ventricular activity; high-voltage pulse delivery electrodes, coupled with the high-voltage inverter circuit; circuits for, respectively, delivering high-energy, defibrillating pulses, and providing PDF information signals; a pulse counter/memory for counting and storing the number of defibrillating pulses issued by the inverter circuit; a piezoelectric speaker, coupled to the wall of a case enclosing the defibrillator circuits, for generating audible tones indicative of the status of the defibrillator; and means responsive to an external magnet for changing the state of the defibrillator.
Technology now exists for the development of implantable devices capable of both pacing and cardioverting, each in response to a sensing mechanism which is incorporated in the implantable device. The electrodes for sensing cardiac electrical abnormalities, as well as for delivering electrical impulses to the heart, are an extremely important consideration in the entire pacing/cardioverting system. U.S. Pat. No. 3,942,536 to Mirowski et al discloses a single intravascular catheter electrode system which monitors heart function and provides the malfunctioning heart with electrical shocks of sufficient amplitude to restore the heart to normal sinus rhythm.
U.S. Pat. No. 4,030,509, issued to Heilman et al, discloses several embodiments of an electrode system for use in ventricular defibrillation wherein the electrodes are applied to the exterior surface of the heart.
U.S. Pat. No. 4,161,952, issued to Kinney et al, discloses a catheter electrode including a resilient, wound wire discharge electrode having proximal and distal ends. The proximal end of the lead is adapted for connection to a pulse generator. The lead is connected to the wound wire discharge electrode both at the proximal and distal ends thereof, and the catheter electrode system is designed for positioning in the superior vena cava or in the coronary sinus, and preferably acts against an independent apex electrode. Thus, the electrode system of Kinney et al is not of unitary design.
U.S. Pat. No. 4,355,646, issued to Kallok et al, discloses a lead having multiple electrodes which is intravenously implanted for use in patients having a high risk of ventricular fibrillation. The lead comprises four electrodes, the two distal electrodes being spaced for optimal measurement of impedance changes due to mechanical contractions and used for mechanical sensing of normal cardiac activity. The two proximal electrodes are spaced from the distal electrodes so as to ensure their placement within the superior vena cava; the two distal electrodes serve to deliver the defibrillation energy.
None of the prior art references noted above discloses an effective multiple electrode unitary intravascular catheter capable of sensing heart abnormality and delivering either defibrillating energy or pacing energy in response to the abnormality for restoring normal heart function.
Additionally, none of the prior art devices noted above is capable of delivering a high-energy discharge through a single catheter and immediately being able to effectively sense the heart's electrical activity through the same catheter. Following cardioversion, the tissue in the area immediately adjacent the discharge electrodes at least temporarily loses a substantial portion of its ability to conduct electrical impulses due to the high electrical energy just applied to the area. Full recovery most often results, but there is a time when electrical conduction suffers. This phenomenon deleteriously impacts on the sensing capability of the prior art devices which sense and cardiovert from the same two electrodes, at least at a time when sensing is of utmost importance.
Further, the prior art electrodes were somewhat limited in their capability for integration with other electrodes in the event that pacing, cardioverting, or sensing could more effectively be accomplished through alternate electrode configurations.
Thus, a need has continued to exist for a unitary multiple electrode catheter capable of sensing, pacing and cardioverting the heart, with an improved sensing capability immediately following cardioversion, and having the flexibility to permit integration with other electrodes in the event that a more effective distribution of the electrical energy is attainable.